Most of the methods described in the prior art for the reaction of olefins with carbon monoxide and water to form the corresponding carboxylic acids either require extreme reaction conditions or produce the desired acids in very low yield. Recently, however, it has been shown that bromide- or iodide-promoted rhodium compounds are effective catalysts for the hydrocarboxylation of olefins under relatively mild conditions.
In U.S. Pat. No. 3,579,552, Craddock et al. disclose a process for the preparation of carboxylic acids by the reaction of ethylenically unsaturated compounds with carbon monoxide and water, in the presence of catalyst compositions essentially comprising rhodium compounds and complexes, together with an iodide promoter.
In U.S. Pat. No. 4,690,912, Paulik et al. disclose a bromide- or iodide- promoted rhodium catalyst system for the carbonylation of carbonylatable reactants.
In U.S. Pat. No. 4,622,423, Burke discloses the preparation of 3-pentenoic acid by hydrocarboxylating butadiene with carbon monoxide and water in the presence of a rhodium-containing catalyst, an iodide promoter and certain halocarbon solvents. Methylene chloride is the preferred solvent; acetic acid in aqueous solution is said to be undesirable.
In U.S. Pat. No. 4,788,334, Burke discloses a process for the hydrocarboxylation of linear olefinically unsaturated esters and terminally unsaturated alkenes having 4 to 16 carbon atoms to form a mixture which contains an increased amount of the linear carboxylate acid. The reaction mixture comprises the ester or the terminally unsaturated alkene, carbon monoxide, water, a halocarbon or aromatic solvent, a rhodium catalyst, an iodide promoter and a mildly acidic accelerator.
Although the prior art does disclose the use of halide-promoted rhodium catalysts for the hydrocarboxylation of butadiene, there is still a need for a process in which butadiene can be hydrocarboxylated in high yields with high linear selectivity and at high rates. The object of this invention is to provide such a process for the preparation of 3-pentenoic acid, a potential precursor to the commercially important dicarboxylic acid, adipic acid.